1. Field of the Invention
The present invention relates to an oil free screw compressor having a compressor airend compressing a gas such as an air or the like, a driving apparatus driving the compressor airend, a cooling device cooling the gas discharged from the compressor airend and the like, and is particularly suitable for a middle capacity package type oil free screw compressor provided with a low pressure stage compressor airend and a high pressure stage compressor airend.
2. Description of Related Art
As one example of the conventional middle capacity oil free screw compressor, there is a structure described in patent document 1 (JP-A-2002-155879 (FIG. 1)). In this conventional structure, a gear shaft within a gear casing and a motor shaft driving the gear shaft are coupled by using a coupling. Further, generally, the motor and the gear casing are both fixed to a driving system special purpose base fixed to a common base, and cooling devices such as an air-cooled cooler (an after cooler, an inter cooler, an oil cooler or the like) and the like is arranged in a back surface of the compression main body or a driving system apparatus (a motor, a gear casing or the like). The cooler constructing the cooling device is arranged so as to be exposed to a back surface of a package, and is structured such as to directly take a low-temperature ambient air into the cooler, thereby achieving a downsizing.
Further, such as a prior art described in patent document 2 (JP-A-11-141488 (FIGS. 2 to 8), there has been known a structure in which the inter cooler, the after cooler, the oil cooler or the like is arranged in one side which is isolated from the compression main body and the driving system apparatus within the package, the motor and the compressor airend are fixed to the gear casing, and the gear casing is fixed to the base.
In both of the conventional oil free screw compressors, since the structure is made such that the gear casing and the motor are fastened by using the coupling, and the motor and the gear casing are both provided with the driving system special purpose base fixed to the common base, and are fixed thereto, it takes a lot of trouble to regulate so as to center the coupling, and a unit length is elongated. Further, there is a disadvantage that the driving system special purpose base, the gear shaft, the gear shaft bearing and the like are necessary.
Since the gear casing doubles as a function of an oil reservoir, the gear casing is enlarged in size, so that there is a problem that a high cost is involved by a necessity of a great working equipment. Further, since the gear casing is large, it is known that the gear casing itself is vibrated like a drum so as to form a noise source.
Further, in the package-shaped oil free screw compressor or the like, since the structured is generally made such that the device such as the cooler or the like constructing the cooling apparatus is exposed to a back surface of the package, or is directly communicated, there is a disadvantage that a vibration sound or a pulsation sound tends to leak to an outer side of the package from a surface of the cooler portion.